The generation of residual water in industrial and agro-industrial processes as well as in commercial businesses and residences is something worrisome when the issue is analyzed through the environmental aspects involved.
Residual water essentially consists of the community supply water, after having served a variety of uses and may be defined as a combination of liquids or water transporting residues removed from residences, commercial and industrial businesses, several institutions and, in the rural environment, animal facilities, agro-industries, etc.
If the residual water is accumulated, the decomposition of organic material may lead to the production of big quantities of smelly gases. In addition to this, untreated residual water usually contains numerous pathogenic microorganisms which inhabit the human or animal intestinal tract, or which may be present in certain industrial residues. Residual water also contains nutrients that can stimulate the growth of aquatic plants but they can also contain toxic components. Therefore, the immediate removal of residual water from the generating sources, followed by its treatment and disposition is not only desirable but it is also necessary in a society concerned about health issues.
The spill of residual water without a previous treatment has been causing the contamination of the soil, as well as superficial and subterraneous water, being a hazard to public health and bringing different damage and discomfort to human beings and animals besides the emission of gases that affect the whole environment and the quality of life.
Biodigestors and the anaerobic ponds are facilities aiming to provide the physical storage of organic dejects in which the biochemical transformations related to the anaerobic biodigestion process of the organic fraction contained in residual water take place. The bacteria and the methanogenic Archaea are the main cause for the organic fraction degradation and, in the anaerobic processes biogas is produced, which consists mainly of methane. The anaerobic systems cater for a number of residues with organic characteristics found both in the urban and rural environments, making them an important option for the treatment and stabilization of organic matter and for generating biogas.
This gas can be used in direct combustion or as fuel for alternative motors, to generate electrical power or for several kinds of equipment used in water and gas heating and cooling.
Several types of systems for the suitable treatment of residual water have been created. However, due to the volumes generated, the high costs make it difficult for the systems to be applied on a large scale.